Several factors may affect your thinking as you decide how important last night's voting was. Turnout was low, and no convention delegates were awarded as Missouri held a primary, and Minnesota and Colorado held caucuses.

MONTAGNE: Then again, nobody awarded delegates when Iowa voted, either. The fact is, people voted, and Rick Santorum won all three states.

INSKEEP: And as good as the news was for Santorum, it was equally bad for Mitt Romney, facing yet another challenge in his drive for the nomination.

DON GONYEA, BYLINE: Rick Santorum was beaming as he leapt onto the stage at his night party in St. Charles, Missouri last night.

(SOUNDBITE OF CHEERING)

GONYEA: The first word out of his mouth....

(SOUNDBITE OF RALLY)

RICK SANTORUM: Wow.

(SOUNDBITE OF CHEERING)

GONYEA: At this point, the Colorado result wasn't yet in, but Santorum already had plenty to celebrate. Expectations had been far exceeded.

(SOUNDBITE OF RALLY)

SANTORUM: Conservatism is alive and well in Missouri and Minnesota.

(SOUNDBITE OF CHEERING)

GONYEA: Santorum then gave a shout out to social conservatives and to the Tea Party, groups that have never liked Mitt Romney, but who have not previously coalesced behind Santorum as an alternative the way they did yesterday.

(SOUNDBITE OF RALLY)

SANTORUM: If you've listened to our message and you've found out that on those issues - health care, the environment, cap and trade, and on the Wall Street bailouts - Mitt Romney has the same positions as Barack Obama, and, in fact, would not be the best person to come up and fight for your voices for freedom in America.

(SOUNDBITE OF CHEERING AND APPLAUSE)

GONYEA: Breaking down the numbers in Missouri, Santorum benefited from low turnout and the fact that his conservative rival Newt Gingrich had failed to meet requirements to get on the ballot. Missouri was a non-binding beauty contest, so the other candidates also paid little attention.

Santorum's performance in Minnesota was more impressive. The ballot had all the candidates. Mitt Romney had won there four years ago. But the upstart challenger prevailed with backing from the same voters who helped him win in neighboring Iowa last month: evangelicals.

Most impressive of all for Santorum was his victory in Colorado. As part of the West, this was seen as a Romney stronghold. But after a vote tally that went back and forth for hours, Santorum was declared the winner by five percentage points. Romney's confidence in Colorado was reflected in the fact that he held his election night party in Denver. It was supposed to be a victory party.

Romney spoke after the Missouri and Minnesota results were in, but Colorado was still up in the air at the time.

(SOUNDBITE OF SPEECH)

MITT ROMNEY: This was a good night for Rick Santorum. I want to congratulation Senator Santorum, wish him the very best. We'll keep on campaigning down the road. But I expect to become our nominee with your help.

(SOUNDBITE OF CHEERING)

GONYEA: Bad as they were for Romney, the night's results do not knock him off as frontrunner. There's simply no one else who can claim that title. He has the biggest organization, the most money, and the ability to buy TV ads and run an aggressive campaign in every state. That's more than rivals Ron Paul and Newt Gingrich can do. Paul's best finish yesterday was a second place in Minnesota, while Gingrich had a third in Colorado, a fourth in Minnesota and failed to get on the ballot in Missouri.

But it's still a dog-fight, as Romney's opposition keeps finding ways to re-energized itself.